Sadly there are only really three (and a half) options for integrating lightning into an existing application - (full) LDK, ldk-node, greenlight/breez, and (kinda) LND. Integrating LND into an existing application is a ton of work, and lots to maintain, so generally hasn't been something people do, or have stuck with long-term.

The full LDK interface is a lot of work, but very flexible in terms of how it gets integrated into an existing application, with customization for how/where you store your data, how you generate all key material, how/where you get blockchain data from, how/where you do signing operations, several different models of potential watchtower integration, etc, etc. This is great if you need some of that customization, but if not its a lot of work just to build the same thing everyone else has.

ldk-node is a standard node that does all the usual things to build a lightning node, packaged up with a super simple API (start node, open channel, pay money, list transactions) that handles storage and keys and blockchain sync for you. It works great on mobile, and has some flexibility, but is generally targeted at devs who just want something that just works.

greenlight/breez SDK are fairly similar to ldk-node in their API design, but unlike ldk-node they rely on hosting from greenlight/blockstream and integration with the breez LSP, rather than being able to choose your own.